In order to effectively utilize heat discharged from factories, automobiles, electronic equipment, etc., a thermoelectric conversion device for converting thermal energy to electric energy is being studied.
When a temperature difference is provided between one end and another end of a semiconductor, a thermoelectromotive force is generated between one end and another end of the semiconductor. For example, when the temperature at one end of an n-type semiconductor is made higher than the temperature at another end, a carrier on the high temperature side transfers to the low temperature side (another end), and a thermoelectromotive force is thereby generated. Similarly, when a temperature difference is provided between one end and another end of a p-type semiconductor, a thermoelectromotive force in an opposite direction to that in the case of an n-type semiconductor is generated.
In a conventional thermoelectric conversion device, a temperature difference (gradient) between a high temperature region and a low temperature region, i.e., a difference in the average kinetic energy of majority carrier, works out to a driving force (Seebeck effect). For example, when a temperature difference between a high temperature region and a low temperature region is 300 K, the temperature difference is converted to an average kinetic energy of approximately 28 meV, and the output of a single device is consequently less than 50 mV. The device can be therefore hardly used as a power device only by joining an electrode to both ends of an n-type semiconductor or a p-type semiconductor. Accordingly, various efforts are being undertaken to use the device as a power device.
For example, Patent Document 1 discloses a so-called π-type thermoelectric conversion device. In the π-type thermoelectric conversion device, a common electrode is attached to one end of an n-type semiconductor and one end of a p-type semiconductor, and individual electrodes are attached respectively to another end of the n-type semiconductor and another end of the p-type semiconductor. By establishing such a configuration, a total thermoelectromotive force of a thermoelectromotive force induced by the n-type semiconductor and a thermoelectromotive force induced by the p-type semiconductor is obtained. In addition, Patent Document 1 discloses using an n-type semiconductor prepared by dispersing a transition metal or a silicide of a transition metal in Mg2Si1-xSnx doped with Bi, etc.